Understanding the concepts presented in this chapter will enable the student to:
Describe the structure and function of the following cellular components of
cardiac myocytes: sarcolemma, intercalated disks, transverse (T)-tubules,
myofilaments, sarcomeres, sarcoplasmic reticulum, and terminal cisternae.
List the steps of excitation-contraction coupling, and describe the cellular
mechanisms involved in its regulation.
List in order of preference the metabolic substrates used by the heart, and
summarize the importance of oxidative metabolism relative to anaerobic
Describe the major histological structures of a muscular artery and the function
of these structures.
Contrast the organization of actin and myosin in vascular smooth muscle with
the organization of these myofilaments in cardiac myocytes.
Describe the mechanisms and regulation of vascular smooth muscle contraction
Compare the major G-protein signal transduction pathways of cardiac muscle
and vascular smooth muscle and how these pathways regulate contraction.
Describe the effects of endothelial-derived nitric oxide (NO), prostacyclin
(PGI2), and endothelin-1 (ET-1) on vascular function.
Many different cell types are associated with
the cardiovascular system. This chapter exam-
ines the structure and function of three major
types of structural cells that serve important
roles in cardiovascular function: cardiac myo-
cytes, vascular smooth muscle, and vascular
CARDIAC CELL STRUCTURE
Myocytes and Sarcomeres
Cardiac myocytes represent a type of stri-
ated muscle, so called because crossbands or
cross striations are observed microscopically.
Although cardiac muscle shares some struc-
tural and functional similarities with skeletal
muscle, it has several important differences.
Cardiac myocytes are generally single nucle-
ated and have a diameter of approximately
25 (tm and a length of about 100 jlm in the
ventricle (atrial myocytes are smaller). In con-
trast, although some types of skeletal muscle
myocytes may have a similar diameter, their
cell lengths run the entire length of the mus-
cle and therefore can be many centimeters
long. Cardiac myocytes form a branching net-
work of cells that is sometimes referred to as
a functional syncytium, which results from
a fusion of cells. Individual myocytes con-
nect to each other by way of specialized cell
membranes called intercalated disks.
junctions within these intercellular regions